   {:arglists '([opts? relations+])}
   [& opts-relations]
   (let [[opts relations] (split-opts-relations opts-relations)]
-    (raw/distinct$ (raw/union$ relations {}) opts)))
+    (raw/distinct$ (raw/union$ (filter identity relations) {}) opts)))
 
 (defn concat
   "Concatenates all relations provided. Does not guarantee any ordering of the

"
  {:arglists '([relations+])}
  [& relations]
  (raw/union$ relations {}))

(defn union-multiset
  "Performs a union on all relations provided and returns all results.

"
  {:arglists '([relations+])}
  [& relations]
  (raw/union$ (filter identity relations) {}))

(defn intersection
  "Performs an intersection on all relations provided and returns the distinct
